Embodiments of the invention relate generally to synthetic jet devices and, more particularly, to an apparatus for increasing the volumetric flow rate and heat transfer rate of synthetic jet devices.
Synthetic jet actuators are a widely-used technology that generates a synthetic jet of fluid to influence the flow of that fluid over a surface to disperse heat away therefrom. A typical synthetic jet actuator comprises a housing defining an internal chamber. An orifice is present in a wall of the housing. The actuator further includes a mechanism in or about the housing for periodically changing the volume within the internal chamber so that a series of fluid vortices are generated and projected in an external environment out from the orifice of the housing. Examples of volume changing mechanisms may include, for example, a piston positioned in the jet housing to move fluid in and out of the orifice during reciprocation of the piston or a flexible diaphragm as a wall of the housing. The flexible diaphragm is typically actuated by a piezoelectric actuator or other appropriate means.
Typically, a control system is used to create time-harmonic motion of the volume changing mechanism. As the mechanism decreases the chamber volume, fluid is ejected from the chamber through the orifice. As the fluid passes through the orifice, sharp edges of the orifice separate the flow to create vortex sheets that roll up into vortices. These vortices move away from the edges of the orifice under their own self-induced velocity. As the mechanism increases the chamber volume, ambient fluid is drawn into the chamber from large distances from the orifice. Since the vortices have already moved away from the edges of the orifice, they are not affected by the ambient fluid entering into the chamber. As the vortices travel away from the orifice, they synthesize a jet of fluid, i.e., a “synthetic jet.”
One drawback of typical synthetic jet devices is that they generate very low flow rates, so as to only provide for a corresponding low heat transfer rate. This low heat transfer rate can be problematic for systems and devices that require high rates of heat dissipation. Particularly in electronics packages, the rise in heat dissipation levels associated with increasingly powerful processing system has resulted in the need for improved cooling rates that typical synthetic jet devices may not be able to meet. In the microelectronics industry, for example, advances in technology have brought about an increase in transistor density and faster electronic chips, such that the heat flux that must be dissipated to maintain reasonable chip temperatures has also risen. While increasing the size and/or number of synthetic jet devices to meet these increased cooling requirements is possible, it is recognized that there are often severe volume constraints imposed on any cooling systems implemented to cool such electronic packages.
Accordingly, there is a need for a system for cooling heat-producing devices in an efficient manner. There is a further need for such a system to have minimal space requirements and provide an increase in the cooling flow rate.